It is exceedingly rare where malware will jump drives, all I can think of is that the registry was changed in some obscure place to disable the CD/USB

Sanitise the USB’s with this

Download McShield to your desktop and install
It will initially run a scan and show the result as a toaster by the system clock
Then in the control centre select scanner and tick unhide items on flash drives

https://dl.dropbox.com/u/73555776/mcshield%20unhide.JPG

Plug in the drive and McShield will start a scan

Then get the log which will be here :

Start > all programs > MCShield > logs > all scans

And post that